1. Field of the Invention
The present invention relates to a process for producing a granular bleach activator composition having excellent solubility and storability, and also to a granular bleach activator composition.
2. Description of the Related Art
Various bleach activators have been proposed for improving the bleaching power of oxygenic bleaching agents such as sodium percarbonate (hereinafter referred to as PC occasionally) and sodium perborate (hereinafter referred to as PB occasionally). However, the functions of bleach activators are seriously impaired by the interactions with the oxygenic bleaching agent or other components of the detergent during storage. Therefore, bleach activators must be protected from its surroundings by granulation, surface coating or the like. However, any protective means which is utilized should not cause a deterioration in the dispersibility or solubility of the bleach activators in washing water.
Many investigations have been made in the prior art in order to satisfy these requirements for bleach activators. For example, U.S. Pat. No. 4,444,674 ("granular bleach activator composition", published on Apr. 24, 1984, PROCTER & GAMBLE Co., Ltd.) discloses a process for producing a lump bleach activator composition having good stability and high dispersibility by spraying a liquid binder and then a water-insoluble silica or silicate on the bleach activating component in a pan granulator. U.S. Pat. No. 4,695,397 ("granular bleach activator", published on Sep. 22, 1985, BASF AG) discloses a process for producing a granular bleach activator composition having good solubility by compression-molding a bleach activator, an expansible solubilizer and a dispersant on an extrusion granulator and then pulverizing and classifying the product. U.S. Pat. No. 4,681,695 ("bleach activator composition", published on Jul. 21, 1987, PROCTER & GAMBLE Co., Ltd.) discloses a process for producing a granular bleach activator composition by spray drying a bleach activator and a water-soluble or inorganic hydratable substance. European Patent No. 63512 ("granulated bleaching agent, process for producing the same and use thereof for a detergent bleach composition") discloses a process for granulating tetraacetylethylenediamine and an alkali metal polyphosphate by using an aqueous solution of sodium carboxymethylcellulose as a binder.
The conventional granular bleach activator compositions as described above have good storage ability when they are stored alone and they are relatively rapidly dissolved in water when warm water is used for washing as in the U.S.A. and in European countries. As in most cases in Japan, however, when washing is conducted under the condition of weak agitation in cold water or when bleaching is conducted under the condition where scarcely any stirring force is applied, such as under mere immersion, the conventional granular bleach activator composition will have such a low dissolution velocity that the functions of the bleach activators cannot be sufficiently exhibited. When the conventional granular bleach activator composition is blended with PC or PB, the reaction of PC or PB with the bleach activator occurs to impair the storability of the composition.